Technical Details of Hexagonal ConnectionStructural Geometry• External hexagon (core shaft): Regular hexagonal outer profile with six equal flat surfaces is milled on the working section of the core shaft. • Internal hexagon (screw element): Regular hexagonal inner bore is machined on conveying, kneading and mixing elements. • Torque is transmitted through the six flat side surfaces. Centering relies on the outer circle of hexagon. Axial positioning and locking of elements are realized by lock nuts and retaining rings. • Comparison - vs Single key: Only one working surface carries load for single key; six surfaces share torque for hexagonal connection, achieving higher load capacity.
- vs Rectangular spline: Rectangular spline consists of multiple straight teeth; hexagonal connection adopts integral polygonal profile without separate thin teeth.
- vs Involute spline: Involute spline realizes multi-tooth meshing with high tooth root strength; hexagonal connection suffers severe stress concentration at corners.
Material Configuration• Core shaft: 40CrNiMoA, quenched & tempered + surface hardening to enhance wear resistance of six hexagonal flat surfaces. • Screw element body: 38CrMoAlA, WR5, WR13. Manufacturing Process• Mill hexagon after forging and quenching & tempering of core shaft. • Boring and broaching to machine hexagonal inner bore on screw element blanks. • Fillet transition at hexagonal corners to reduce stress concentration. Process Parameter Characteristics• Torque capacity: Low-medium torque. Lower than rectangular spline and far lower than involute spline. Not suitable for high specific torque main extruders. • Centering accuracy: Moderate. Circumferential clearance expands rapidly and phase offset occurs once corners are worn. • Interchangeability: Poor. Highly sensitive to machining errors of across-flat dimension and angles, poor cross-machine interchangeability. • Assembly & disassembly: Elements can slide axially for mounting and removal. • Failure modes: Crushing of hexagonal corners and side surface wear, which are typical failures of this structure. | Functions of Hexagonal Connection•Transmit rotational torque. Six flat surfaces bear torque simultaneously to transfer torque from core shaft to all screw elements. Applied to medium alternating torque conditions on small machines and pilot lines. •Modular screw assembly. Screw elements can slide axially. Elements can be rearranged, added or removed freely to adjust screw process configuration. Special machines with 24-sided inner bore support multi-gear fine adjustment of phase. | 
